# Homework Help: Reynolds number

1. Dec 22, 2009

### tomwilliam

1. The problem statement, all variables and given/known data
Estimate a reynolds number for a pipe of 0.3m internal diameter, carrying water at a rate of 71 m/s, and say what that says about the likely nature of the flow.

2. Relevant equations
Re = (density x L x velocity of flow)/coefficient of dynamic viscosity for water
Viscosity of water = 8.9 x 10^-4 kg/m s
density of water = 1000 kg/m^3

3. The attempt at a solution

Well, I have produced a result of some 27 million, which seems excessive to me. Possible mistakes: I used the diameter of the pipe as L. Also, the flow speed is something I calculated in a previous question, so could potentially be wrong. The speed is just due to potential energy coming from a reservoir exactly 500m higher up, where pressure is atmospheric only.
Does anything sound wrong with this solution? I have no reference for typical reynolds numbers in these situations...

2. Dec 22, 2009

### denverdoc

I got a similar result.

3. Dec 22, 2009

### tomwilliam

Thanks - In that case I'd better check that I've got the right flow speed for a height difference of 500m and a diameter of 0.3m.

4. Dec 22, 2009

### denverdoc

I just used one of those on-line RN calculators--I got 23.9 million which is close, esp in the world of Reynolds numbers--certainly the answer to the next question will be the same.